1. Field of the Invention
The present invention relates to a method of preparing an MMC (metal matrix composite material), and more particularly, to a method of preparing an aluminum matrix particle composite alloy containing ceramic particles by powder forging.
2. Background Information
An MMC, which has mechanical strength and physical characteristics (Young's modulus etc.) equivalent to those of iron, titanium etc. and is lightweight, can usefully be substituted for iron or titanium as a component material for household electrical apparatus, business machines, robots etc.
MMCs can be prepared by either of two methods, i.e., casting and powder metallurgy. Casting includes long fiber reinforcing, short fiber reinforcing and particle reinforcing methods. On the other hand, powder metallurgy includes only short fiber reinforcing and particle reinforcing. Using powder metallurgy, it is possible to obtain a matrix alloy with a higher degree of freedom. The alloy prepared by the powder metallurgy method has a higher strength compared to the casting method, thereby obtaining a highly reliable component without mold cavity casting defects. However, powder metallurgy has the disadvantage that mixed reinforcing particles segregate in old powder boundaries and the particles themselves are large even if no segregation takes place. Casting also has problems of gravity segregation in solidification and the size of particles.
In order to prepare an MMC in which reinforcing particles are homogeneously dispersed, the particles are generally added by a mixing method, which is economical, easy and effective in improving physical characteristic values. Using this method, however, it is difficult to attain sufficient dispersion/reinforcement in the case of simple mixed powder since the dispersed particles are present in the old powder boundaries, while the particles are inhibited from bonding when fine particles are dispersed. Also in casting, particles are heterogeneously dispersed since the dispersed particles move to slowly solidified portions due to gravity segregation in solidification and the slow solidification rate.
Thus, none of the conventional methods can provide an MMC which has acceptable characteristics and is economical to produce, and hence no MMC has been put into practical use. It is most important for an MMC to obtain extra-fine reinforcing particles while homogeneously distributing them without segregation.
Furthermore, an MMC is generally inferior in machinability due to the dispersion of hard particles. Thus, it is important to form MMC materials into a near net shape, i.e., a shape close to that of the final product. Therefore, it is necessary to select and specify powder characteristics allowing for the use of a conventional powder metallurgy process or the like.